Conventionally, electronic devices including a circuit board and electronic components mounted on the circuit board have been used in electronic apparatuses.
Japanese Unexamined Patent Publication JP-A 11-214449 (1999) discloses an electronic device including a circuit board and a bare chip mounted on the circuit board in a flip-chip manner.
In this way, when a bare chip is flip-chip mounted on a circuit board and heat is applied to the electronic device at the time of mounting the bare chip or during working, thermal stress may be generated in a connecting portion of the circuit board and the bare chip due to the difference in coefficient of thermal expansion between the circuit board and the bare chip, the thermal stress may be applied to electrodes of the bare chip having low durability to break the electrodes, and the electrical reliability of the electronic device may be easily lowered.
On the other hand, Japanese Unexamined Patent Publication JP-A 2004-311574 discloses an electronic device including a circuit board, an electronic element mounted on the circuit board, and an interposer interposed between the circuit board and the electronic element, wherein the interposer includes a substrate formed of an inorganic material (inorganic insulating material) having an insulating property, and a conductor-built-in through-hole penetrating the substrate and having a conductor filled in a penetrated portion.
In this way, since the interposer having a substrate formed of an inorganic insulating material can more easily reduce the difference in coefficient of thermal expansion from that of the electronic element, compared with the circuit board, thermal stress generated in the connecting portion between the interposer and the electronic element can be reduced and the thermal stress applied to electrodes of the electronic element can be reduced.
However, the inorganic insulating material having a small difference of the coefficient of thermal expansion from that of the electronic element has a smaller coefficient of thermal expansion than that of the conductor. Accordingly, when heat is applied to the electronic device, the conductor-built-in through-hole may thermally expand more than the substrate, the conductor may be peeled off from the inner wall of the through-hole and protrude from the substrate, and the connecting portion between the interposer and the electronic element may be broken due to the protrusion, thereby easily lowering the electrical reliability of the electronic device.
Therefore, there is a need for providing an interposer with improved electrical reliability.